Heat the oil in a pan on medium heat. Once hot add mustard seeds. Let them pop.
Now add green chilies and saute for a minute.
Add mint leaves. Cook for 2 minutes only. The leaves will start to wilt. Do not overcook.
Let it cool down slightly.
In a grinder jar, take grated coconut, add above cooked mint leaves, salt and tamarind paste. Start with ½ cup of water and add little more later as needed.
Grind into smooth paste.
Remove it to a serving bowl and serve.
Notes
Do not overcook mint leaves otherwise mint will lose its flavor and color.For a variation, you can try substituting the tamarind with lemon juice. Lemon juice gives more tang to the chutney. You can also add 2-3 tablespoons of roasted bengal gram (dalia) while grinding.